Local drug delivery for the prevention of restenosis. Fact, fancy, and future

New Devices and Technologies for Hemodialysis Vascular Access: A Review

In the United States, hemodialysis remains the most common treatment modality for kidney failure, chosen by almost 90% of incident patients. A functioning vascular access is key to providing adequate hemodialysis therapy. Recently, major innovations in devices and technology for hemodialysis vascular access care have rapidly changed the landscape. Novel endovascular devices for creation of arteriovenous fistulas may offer a solution to the barriers encountered in initiating maintenance hemodialysis with a permanent vascular access rather than a central venous catheter (CVC). Furthermore, in the prevalent hemodialysis population, the minimally invasive endovascular arteriovenous fistula procedure should help improve long wait times for vascular access creation, which remains a major barrier to reducing CVC dependence. Bioengineered grafts are being developed and may offer another option to polytetrafluoroethylene grafts. Early studies with these biocompatible grafts are promising, as additional studies continue to evaluate their clinical outcomes in comparison to cryopreserved or synthetic options. Prolonging the vascular access patency with appropriate use of devices such as drug-coated balloons and stent grafts may complement the novel techniques of creating arteriovenous access. Finally, innovative solutions to treat stenosed and occluded thoracic central veins can provide an approach to creating a vascular access and allow patients with exhausted vasculature to remain on hemodialysis. The robust developments in hemodialysis vascular access are likely to change practice patterns in the near future.

Survival of Endothelial Cells in vitro on Paclitaxel-loaded Coronary Stents

Coronary stents that are developed for use with balloon angioplasty are known to cause acute occlusion and long-term stenosis. It is likely that a controlled release of drugs at the site of stent implantation might inhibit the proliferation of vascular smooth muscle cells (VSMC) and reduce restenosis. However, if the drug is necrotic and affects cell survival near the implant, it may interrupt the local tissue regeneration. Different methods have been used for the immobilization of drugs with stents to get an effective concentration that inhibits cell proliferation. The objective of this study is to assess the effectiveness of Paclitaxel-loaded stents by immobilization with a biodegradable polymer, to inhibit cell proliferation. The cells used for the evaluation are human umbilical vein endothelial cells (HUVEC) and the proliferation rate of these cells on the drug-coated stent is compared against an uncoated stent for a 72-h period. Evaluations were also made to differentiate between cell apoptosis and necrosis to prove that the drug released is not deleterious to the surrounding tissue.

While a similar initial cell adhesion is observed in bare and coated stents, the proliferation of HUVEC is negligible when grown on a drug-coated stent (p < 0.001). By specific staining techniques, the cells on the drug-coated stents are found to be apoptotic and not necrotic, throughout the evaluation period. In vitro leukocyte adhesion and platelet deposition on the drug-coated stents are found to be low when they are exposed to human blood and platelet-rich plasma (PRP), suggesting that the coated stents may not be thrombogenic in vivo. Therefore, drug coating of stents using the described technique may have a considerable promise for the prevention of neointimal proliferation, restenosis, and associated failure of angioplasty.

Perspective and potential of oral lipid-based delivery to optimize pharmacological therapies against cardiovascular diseases

Cardiovascular diseases (CVDs) remain the major cause of morbidity and mortality globally. Despite the large number of cardiovascular drugs available for pharmacological therapies, factors limiting the efficient oral use are identified, including low water solubility, pre-systemic metabolism, food intake effects and short half-life. Numerous in vivo proof-of-concepts studies are presented to highlight the viability of lipid-based delivery to optimize the oral delivery of cardiovascular drugs. In particular, the key performance enhancement roles of oral lipid-based drug delivery systems (LBDDSs) are identified, which include i) improving the oral bioavailability, ii) sustaining/controlling drug release, iii) improving drug stability, iv) reducing food intake effect, v) targeting to injured sites, and vi) potential for combination therapy. Mechanisms involved in achieving these features, range of applicability, and limits of available systems are detailed. Future research and development efforts to address these issues are discussed, which is of significant value in directing future research work in fostering translation of lipid-based formulations into clinical applications to reduce the prevalence of CVDs.

Peripheral applications of drug-coated balloons: past, present and future

Drug-coated balloon (DCB) technologies represent the latest and hottest development in the field of endovascular treatment of peripheral arterial disease. Initial experience with paclitaxel-coated balloon use in the femoral artery has demonstrated lower mid-term restenosis and superior mid-term clinical outcomes in terms of improved wound healing and reduced repeat angioplasty rates compared with standard balloon angioplasty. Many companies are presently developing and/or improving DCB catheters and therefore ongoing, technical improvements of the already existing platforms, new drugs, and innovative carriers are expected. The ongoing basic research studies and various multicenter randomized, controlled trials that are currently in progress will offer valuable scientific insights regarding the long-term effectiveness and other crucial issues, such as efficacy in various vascular beds, optimal balloon dosage, and post angioplasty antiplatelet therapy. Future applications of these devices also could include in-stent restenosis, anastomotic stenosis of surgical bypass, and benign stenoses of the central venous system. The authors envision that DCB angioplasty will evolve to a major paradigm shift in the endovascular treatment of occlusive vascular diseases.

Perspectives on the role of nanotechnology in bone tissue engineering

OBJECTIVE

This review surveys new developments in bone tissue engineering, specifically focusing on the promising role of nanotechnology and describes future avenues of research.

METHODS

The review first reinforces the need to fabricate scaffolds with multi-dimensional hierarchies for improved mechanical integrity. Next, new advances to promote bioactivity by manipulating the nanolevel internal surfaces of scaffolds are examined followed by an evaluation of techniques using scaffolds as a vehicle for local drug delivery to promote bone regeneration/integration and methods of seeding cells into the scaffold.

RESULTS

Through a review of the state of the field, critical questions are posed to guide future research toward producing materials and therapies to bring state-of-the-art technology to clinical settings.

SIGNIFICANCE

The development of scaffolds for bone regeneration requires a material able to promote rapid bone formation while possessing sufficient strength to prevent fracture under physiological loads. Success in simultaneously achieving mechanical integrity and sufficient bioactivity with a single material has been limited. However, the use of new tools to manipulate and characterize matter down to the nano-scale may enable a new generation of bone scaffolds that will surpass the performance of autologous bone implants.

Nanomedicine approaches in vascular disease: a review

Nanomedicine approaches have revolutionized the treatment of cancer and vascular diseases, where the limitations of rapid nonspecific clearance, poor biodistribution and harmful side effects associated with direct systemic drug administration can be overcome by packaging the agents within sterically stabilized, long-circulating nanovehicles that can be further surface-modified with ligands to actively target cellular/molecular components of the disease. With significant advancements in genetics, proteomics, cellular and molecular biology and biomaterials engineering, the nanomedicine strategies have become progressively refined regarding the modulation of surface and bulk chemistry of the nanovehicles, control of drug release kinetics, manipulation of nanoconstruct geometry and integration of multiple functionalities on single nanoplatforms. The current review aims to capture the various nanomedicine approaches directed specifically toward vascular diseases during the past two decades. Analysis of the promises and limitations of these approaches will help identify and optimize vascular nanomedicine systems to enhance their efficacy and clinical translation in the future.

FROM THE CLINICAL EDITOR

Nanomedicine-based approaches have had a major impact on the treatment and diagnosis of malignancies and vascular diseases. This review discusses various nanomedicine approaches directed specifically toward vascular diseases during the past two decades, highlighting their advantages, limitations and offering new perspectives on future applications.

Production and in vitro characterization of lisinopril-loaded nanoparticles for the treatment of restenosis in stented coronary arteries

Lisinopril, an angiotensin converting enzyme (ACE) inhibitor drug, was encapsulated in poly(lactide-co-glicolide) (PLGA) nanoparticles (NP) for site-specific delivery by catheters in prevention of restenosis. NP were prepared by emulsification-diffusion method. The PLGA type, stabilizing agent type and its concentration were studied as process variables. The z-average particle size varied between 265-412 nm. The highest zeta potential was seen in NP prepared with Pluronic F-68. None of the studied variables or their interactions had a significant effect on the particle size while all had main effect on the zeta potential. The highest entrapment efficiency was 93% and all studied variables and their interactions except PLGA type and its interaction with the stabilizer type had significant effects on the loading. Baker-Lonsdale model was the most appropriate model for release of lisinopril from NP. Five per cent PLGA 75:25 and 5% Pluronic F-68 showed promising results for 21 days release of lisinopril as an anti-restenotic agent.

Effect of a novel drug-eluted balloon coated with genistein before stent implantation in porcine coronary arteries

BACKGROUND

The major drawback of stent implantation in native human coronary vessels is the occurrence of restenosis. Drug-eluting stents significantly reduce restenosis after percutaneous coronary intervention (PCI), but may be associated with persistent local inflammation involved in the restenosis mechanisms. In this setting coating coronary devices with anti-inflammatory agents represents an intriguing alternative to stent-based local drug delivery. The aim of the present study was to test in a porcine model the safety and efficacy of a novel Genistein-eluting balloon preceding coronary stenting.

DESIGN

Female piglets underwent PCI in a randomized fashion with either a Genistein-eluting or a standard balloon angioplasty, followed in all vessels by bare-metal stent implantation. Pigs were sacrificed at different time points to appraise safety (i.e. endothelialization) and efficacy (i.e. anti-inflammatory and anti-proliferative effects): 1, 4, and 6-8 weeks following PCI.

RESULTS

Overall analysis was conducted on 14 piglets. Twenty-five bare-metal stents were implanted preceded by angioplasty with a conventional balloon in 13 vessels and by the Genistein-eluted balloon in 12. No untoward effects were reported in either group. Healing and endothelialization appeared universal within 4 weeks. The Genistein-eluted balloon group disclosed a significant reduction, at four weeks from implantation, of the peri-stent inflammatory cells count (mononucleocytes 39 +/- 32 Vs. 96 +/- 29 per square millimetre, P = 0.019). This effect did not clearly translate into a trend towards a reduced neointimal hyperplasia at 6-8 weeks (0.13 +/- 0.11 Vs. 0.14 +/- 0.09, P = 0.835).

CONCLUSION

This study provides the first in vivo demonstration of the anti-inflammatory effects of a Genistein-eluting balloon in PCI, warranting further research including the combination of a Genistein-eluting balloon with standard drug-eluting stent.

Effect of blood flow on near-the-wall mass transport of drugs and other bioactive agents: a simple formula to estimate boundary layer concentrations

Transport of bioactive agents through the blood is essential for cardiovascular regulatory processes and drug delivery. Bioactive agents and other solutes infused into the blood through the wall of a blood vessel or released into the blood from an area in the vessel wall spread downstream of the infusion/release region and form a thin boundary layer in which solute concentration is higher than in the rest of the blood. Bioactive agents distributed along the vessel wall affect endothelial cells and regulate biological processes, such as thrombus formation, atherogenesis, and vascular remodeling. To calculate the concentration of solutes in the boundary layer, researchers have generally used numerical simulations. However, to investigate the effect of blood flow, infusion rate, and vessel geometry on the concentration of different solutes, many simulations are needed, leading to a time-consuming effort. In this paper, a relatively simple formula to quantify concentrations in a tube downstream of an infusion/release region is presented. Given known blood-flow rates, tube radius, solute diffusivity, and the length of the infusion region, this formula can be used to quickly estimate solute concentrations when infusion rates are known or to estimate infusion rates when solute concentrations at a point downstream of the infusion region are known. The developed formula is based on boundary layer theory and physical principles. The formula is an approximate solution of the advection-diffusion equations in the boundary layer region when solute concentration is small (dilute solution), infusion rate is modeled as a mass flux, and there is no transport of solute through the wall or chemical reactions downstream of the infusion region. Wall concentrations calculated using the formula developed in this paper were compared to the results from finite element models. Agreement between the results was within 10%. The developed formula could be used in experimental procedures to evaluate drug efficacy, in the design of drug-eluting stents, and to calculate rates of release of bioactive substances at active surfaces using downstream concentration measurements. In addition to being simple and fast to use, the formula gives accurate quantifications of concentrations and infusion rates under steady-state and oscillatory flow conditions, and therefore can be used to estimate boundary layer concentrations under physiological conditions.

Anti-inflammatory effect of abciximab-coated stent in a porcine coronary restenosis model

The aim of this study was to examine the anti-inflammatory effect of abciximab-coated stent in a porcine coronary overstretch restenosis model. Ten abciximab-coated stents, ten sirolimus-eluting stents (SES), and ten paclitaxel-eluting stents (PES) were deployed with oversizing (stent/artery ratio 1.3:1) in porcine coronary arteries, and histopathologic analysis was done at 28 days after stenting. There were no significant differences in the neointima area normalized to injury score and inflammation score among the three stent groups (1.58 +/- 0.43 mm(2), 1.57 +/-0.39 mm(2) in abciximab-coated stent group vs. 1.69 +/- 0.57 mm(2), 1.72 +/- 0.49 mm(2) in the SES group vs. 1.92 +/- 0.86 mm(2), 1.79 +/- 0.87 mm(2) in the PES group, respectively). In the neointima, most inflammatory cells were lymphohistiocytes. Significant positive correlations were found between the extent of inflammatory reaction and the neointima area (r=0.567, p<0.001) and percent area stenosis (r=0.587, p<0.001). Significant correlations were found between the injury score and neointimal area (r=0.645, p<0.001), between the injury score and the inflammation score (r=0.837, p<0.001), and between the inflammation score and neointimal area (r=0.536, p=0.001). There was no significant difference in the inflammatory cell counts normalized to injury score among the three stent groups (75.5 +/- 23.1/microL in abciximabcoated stent group vs. 78.8 +/- 33.2/microL in the SES group vs. 130.3 +/- 46.9/microL in the PES group). Abciximab-coated stent showed comparable inhibition of inflammatory cell infiltration and neointimal hyperplasia with other drug-eluting stents in a porcine coronary restenosis model.

Reduction of Stenosis Due to Intimal Hyperplasia After Stent Supported Angioplasty of Peripheral Arteries by Local Administration of Paclitaxel in Swine

PURPOSE

To assess if local intra-arterial administration of paclitaxel using drug-coated balloons or an admixture of paclitaxel to contrast medium inhibits stenosis after percutanous transluminal angioplasty (PTA) of peripheral arteries in a porcine overstretch model.

METHODS

Neointimal proliferation and stenosis were induced by overstretch and stenting of 40 peripheral arteries in 20 pigs. Paclitaxel was administered locally during PTA using coated balloons (n = 20) or dissolved in contrast medium (n = 10). Conventional balloons and contrast medium were used in a control group (n = 10). Reangiography with quantitative analysis was performed after 5 weeks.

RESULTS

On reangiography diameter stenosis and late lumen loss were significantly reduced by both methods of local drug delivery compared with control group; minimal luminal diameter was significantly larger in the treatment groups.

CONCLUSIONS

Local short-term administration of paclitaxel during PTA of peripheral arteries using balloons or contrast medium as drug carriers reduced stenosis due to intimal hyperplasia.

Prevention of restenosis: is angioplasty the answer?

"The drug-coated balloon has the potential to improve the limited results of drug-eluting stents"

A clinical survey of vascular stents

As a result of the many different potential locations to be treated, it is still difficult to evaluate the indications for efficacy and safety of non-coronary percutaneous transluminal angioplasty (PTA) and stenting versus surgical methods, such as endarterectomy or bypass grafts. This paper reviews pertinent data published in the last 5-10 years and gives an overview of the main peripheral minimally invasive vascular interventional fields.

Release of anti-restenosis drugs from poly(ethylene oxide)-poly(DL-lactic-co-glycolic acid) nanoparticles

Dexamethasone- or rapamycin-loaded nanoparticles based on poly(ethylene oxide) and poly(dl-lactic-co-glycolic acid) block copolymers (PEO-PLGA) were prepared without additional stabilizer using the salting-out method. A fast release of drug in PBS (pH 7.4) at 37 degrees C resulting in 100% release within 5 h was observed for both drugs. The rate of drug release was substantially reduced by treating the particles with gelatin or albumin after drug loading, resulting in a linear drug release in time. It was shown that the rate of drug release is related to the amount of protein associated with the nanoparticles. After gelatin treatment of drug-loaded nanoparticles, sustained release of dexamethasone for 17 days and of rapamycin for 50 days could be achieved.

In stent restenosis: bane of the stent era

The long term outcome of stent implantation is affected by a process called in stent restenosis (ISR). Multiple contributory factors have been identified, but clear understanding of the overall underlying mechanism remains an enigma. ISR progresses through several different phases and involves numerous cellular and molecular constituents. Platelets and macrophages play a central role via vascular smooth muscle cell migration and proliferation in the intima to produce neointimal hyperplasia, which is pathognomic of ISR. Increased extracellular matrix formation appears to form the bulk of the neointimal hyperplasia tissue. Emerging evidence of the role of inflammatory cytokines and suppressors of cytokine signalling make this an exciting and novel field of antirestenosis research. Activation of Akt pathway triggered by mechanical stretch may also be a contributory factor to ISR formation. Prevention of ISR appears to be a multipronged attack as no therapeutic "magic bullet" exists to block all the processes in one go.

Role of polyanhydrides as localized drug carriers

Many drugs that are administered in an unmodified form by conventional systemic routes fail to reach target organs in an effective concentration, or are not effective over a length of time due to a facile metabolism. Various types of targeting delivery systems and devices have been tried over a long period of time to overcome these problems. Targeted delivery or localized drug delivery offers an advantage of reduced body burden and systemic toxicity of the drugs, especially useful for highly toxic drugs like anticancer agents. Local drug delivery via polymer is a simple approach and hypothesized to avoid the above stated problems. Polyanhydrides are a unique class of polymer for drug delivery because some of them demonstrate a near zero order drug release and relatively rapid biodegradation in vivo. Further, the release rate of polyanhydride fabricated device can be altered over a thousand fold by simple changes in the polymer backbone. Hence, these are one of the best-suited polymers for drug delivery, with biodegradability and biocompatibility. The review focuses on the advantages of polyanhydride carriers in localized drug delivery along with their degradability behavior, toxicological profile and role in various disease conditions.

Drug-eluting stents: results, promises and problems

In-stent restenosis is the major drawback of percutaneous coronary interventions, occurring in 10-40% of the patients. Recently, new stents have emerged which are loaded with anti-inflammatory, anti-migratory, anti-proliferative or pro-healing drugs. These drugs are supposed to inhibit inflammation and neointimal growth and subsequently in-stent restenosis. In this review article the results of human clinical studies investigating drug-eluting stents are discussed from a clinical point of view, focussing on the efficacy in the prevention of restenosis and their potential side effects. Both success and failure in the field of drug-eluting stents have been described. Successful devices are the sirolimus-eluting and the polymer-based paclitaxel-eluting stents. Potentially dangerous side effects of drug-eluting stents are adverse drug interactions, incomplete stent apposition and increased in-stent thrombosis rates. Demonstration of long-term efficacy is mandatory since in some animal studies a delayed healing has been observed. Currently, the successful drug-eluting stents are under investigation in all types of lesions. We conclude that the results with some drug-eluting stents are promising, but further evidence on long-term efficacy and safety, also in high-risk subgroups, is needed.

Local drug delivery in restenosis injury: thermoresponsive co-polymers as potential drug delivery systems

The success of percutaneous transluminal coronary angioplasty in treatment of acute coronary syndromes has been compromised by the incidence of restenosis. The physical insult of balloon insertion can damage or remove the endothelial monolayer, thereby generating a prothrombotic surface. The resulting inappropriate response to injury can also lead to penetration of inflammatory cells, conversion of the underlying media to a synthetic phenotype, deposition of extracellular matrix, constrictive remodeling, and neointimal hyperplasia. While stent implantation at the time of balloon insertion has offset some of these events, inflammatory responses to the implanted biomaterial (stent) and intimal hyperplasia are still prominent features of the procedure, leading in 20-30% of cases to in-stent restenosis within a year. Systemic delivery of drugs designed to offset in-stent restenosis injury has been largely unsuccessful, which has led to the development of strategies for coating stents with drugs for local delivery. Drug-eluting stents constitute an innovative means of further reducing the incidence of restenosis injury and clinical trials have shown encouraging results. This review focuses on properties of a class of environment-sensitive hydrogels, the N-isopropylacrylamide-based thermoresponsive co-polymers, on their potential roles as stent coatings, on their demonstrated ability to incorporate and release drugs that modify vascular endothelial and smooth muscle cell functions, and on issues that still await clarification, prior to their adoption in a clinical setting.

Estrogen release from metallic stent surface for the prevention of restenosis

For the prevention of coronary restenosis, estrogen was coupled onto a metallic stent and in vitro release of estrogen was investigated. Estrogen was introduced to the metal surface using a hydrolysable covalent bond for local sustained delivery of drug as follows: (i) the stainless steel (SS) surface was activated with silane by plasma polymerization, (ii) the activated surface (SS-Si surface) was treated with acrylic acid by plasma polymerization (SS-Si-AAc surface), and (iii) 17beta-estradiol (E2) was covalently linked to the carboxyl group on that surface (SS-Si-AAc-E2 surface). The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and water contact angle measurement. The amount of E2 was measured by UV-visible spectrophotometry and high performance liquid chromatography (HPLC). The in vitro release profile of E2 demonstrated sustained release of E2 in aqueous buffer. In summary, a novel method of immobilizing estrogen onto a metallic stent surface using plasma polymerization has been developed. The obtained results attest to the usefulness of the estrogen-releasing stent for preventing restenosis.

Novel Echogenic Drug-Immunoliposomes for Drug Delivery

RATIONALE AND OBJECTIVES

We have developed novel echogenic immunoliposomes (ELIPs) that can be antibody-conjugated for the specific highlighting of atheroma and atheroma components. The utility of these agents for regional drug delivery has not been evaluated previously. We chose to use an antibiotic as the prototype drug. The concept that an infectious agent may affect the development and progression of atherosclerosis has stimulated trials on the use of antibiotics for coronary syndromes. However, these agents are given systemically with concomitant problems. Development of an agent for local drug delivery may obviate adverse effects and improve treatment efficacy. The aim of this study was to evaluate the potential of our ELIPs for drug incorporation and to demonstrate efficient drug delivery to cultured cells.

METHODS

Azithromycin was incorporated into the ELIPs during development. Free drug was removed with a Sephadex G-50 column. Acoustic properties were evaluated using an intravascular ultrasound catheter and quantified by computer-assisted videodensitometry. Human umbilical arterial endothelial cells were infected with Chlamydia pneumoniae. Cells were treated with the drug-ELIP complexes, and infection-forming units were counted using fluorescence techniques.

RESULTS

We were able to incorporate a drug into the ELIPs with retention of acoustic properties. The drug-ELIP complex demonstrated effective inhibition of microbial growth in endothelial cells (P < 0.001 vs. empty liposomes and control).

CONCLUSIONS

We have developed a novel acoustic drug-liposomal agent that can deliver drugs to cultured cells. Although in vivo translation is required, this technique has potential for site-specific drug delivery.

Effects of altering infusion parameters on intimal hyperplasia following local catheter-based delivery into the rabbit iliac artery

BACKGROUND

Efficient local gene or drug therapy requires optimized application modalities to avoid vessel damage, which might lead to increased neointimal hyperplasia. Aim of the study was to evaluate different application parameters for local delivery using the channeled balloon catheter in order to minimize vessel trauma induced by local application.

METHODS AND RESULTS

Sixty cholesterol fed rabbits were randomly enrolled into twelve groups of different local application parameters: group I, application pressure 2atm/application volume 1ml physiologic saline; group II, 2atm/2ml; group III, 2atm/5ml; group IV, 4atm/1ml; group V, 4atm/2ml; group VI, 4atm/5ml. The other six groups received Ringer's solution instead of saline. Administration of the solution was randomly performed in one iliac artery using the channeled balloon catheter with simultaneous balloon angioplasty (8atm). The contralateral iliac artery served as a control and was treated with balloon angioplasty only. Four weeks after local therapy, calibrated angiography was performed; the animals were sacrificed, vessel segments were excised and quantitative morphometric measurements were obtained. In none of the animals acute complications, e.g. dissection, thrombosis or perforation of the vessel, was noted. Up to an application pressure of 4atm and an application volume of 5ml, no significant neointima formation was seen compared to arteries which underwent angioplasty only. Additionally, no significant differences between saline and Ringer's solution were detected. In a multivariate analysis, neither application pressure nor volume were found to have a statistically significant influence on the amount of neointimal hyperplasia.

CONCLUSIONS

Local application of "drugs" using the channeled balloon catheter is safe and feasible without significant induction of neointimal hyperplasia compared to angioplasty, if an application volume of 5ml and a pressure of 4atm is not exceeded.

Local intramural delivery of 60% ethyl alcohol for treatment of recalcitrant in-stent restenosis

We report a case of recalcitrant in-stent restenosis after intracoronary brachytherapy failure that was successfully treated with a novel and experimental technique of local intramural delivery of 60% ethyl alcohol.

Heparin release from slippery-when-wet guide wires for intravascular use

Thin metallic wires with an adherent hydrophilic/ lubricious polymeric coating were manufactured in a new extrusion-like procedure. This procedure is part of a novel and efficient way of assembling lubricious guide wires for intravascular interventions, such as percutaneous transluminal angioplasty. It is reported that heparin can readily be incorporated in the hydrophilic coating. A set of heparin-containing guidewire models was made and studied in detail. This showed that (i). immersion of the guide-wire models in an aqueous environment leads to release of heparin from their surface; (ii). the presence of heparin in the coating does not impede the lubricity of the coils; (iii). addition of stearic acid in the coating, next to heparin, does not influence the lubricity of the guide-wire models. Two different charges of heparin (designated heparin-low and heparin-high) were incorporated in the coating. It is discussed that release of heparin from the surface of medical devices (e.g. guide wires and catheters) is much more effective than systemic heparinization, basically because dissolved heparin molecules have a much larger probability of simply passing a medical device's surface (axial convection) rather than contacting it (radial diffusion).

Targeting the cell cycle machinery for the treatment of cardiovascular disease

Cardiovascular disease represents a major clinical problem affecting a significant proportion of the world's population and remains the main cause of death in the UK. The majority of therapies currently available for the treatment of cardiovascular disease do not cure the problem but merely treat the symptoms. Furthermore, many cardioactive drugs have serious side effects and have narrow therapeutic windows that can limit their usefulness in the clinic. Thus, the development of more selective and highly effective therapeutic strategies that could cure specific cardiovascular diseases would be of enormous benefit both to the patient and to those countries where healthcare systems are responsible for an increasing number of patients. In this review, we discuss the evidence that suggests that targeting the cell cycle machinery in cardiovascular cells provides a novel strategy for the treatment of certain cardiovascular diseases. Those cell cycle molecules that are important for regulating terminal differentiation of cardiac myocytes and whether they can be targeted to reinitiate cell division and myocardial repair will be discussed as will the molecules that control vascular smooth muscle cell (VSMC) and endothelial cell proliferation in disorders such as atherosclerosis and restenosis. The main approaches currently used to target the cell cycle machinery in cardiovascular disease have employed gene therapy techniques. We will overview the different methods and routes of gene delivery to the cardiovascular system and describe possible future drug therapies for these disorders. Although the majority of the published data comes from animal studies, there are several instances where potential therapies have moved into the clinical setting with promising results.

New catheter-based technology for the treatment of restenosis

Catheter-based vascular interventions have been in development worldwide for several decades, leading to remarkable progress in device technology. Mechanical interventional devices, such as angioplasty balloons, atherectomy devices, and stents, were invented and have contributed greatly to the treatment of atherosclerotic vascular stenosis. However, mechanical approaches do not effectively prevent subsequent intimal growth. Recently, several biological approaches, including radiation therapy and drug-eluting stents, have shown striking inhibition of intimal growth. These significant results are likely to change the treatment strategy in the field of interventional cardiology. Furthermore, additional catheter-based technologies for vascular interventions are presently being evaluated. These latest technologies designed to prevent intimal proliferation include intravascular sonotherapy, cryotherapy, photoangioplasty, and soft X ray. To date, intravascular sonotherapy has proven its efficacy in animal studies and safety in human studies. Cryotherapy, the application of cold thermal energy during angioplasty, enhances the acute effects of conventional dilation while decreasing the likelihood of restenosis. Photoangioplasty has a unique property based on its selective mechanism of action to treat atheromatous plaque. Soft X ray systems provide convenient device handling and well-controlled radiation dose. Some of these technologies may play an important role in vascular interventions in the near future.

Local delivery of single low-dose of C-type natriuretic peptide, an endogenous vascular modulator, inhibits neointimal hyperplasia in a balloon-injured rabbit iliac artery model

C-type natriuretic peptide (CNP) is an endogenous vascular modulator. In addition to vasodilation, CNP exerts multifunctions including anti-thrombus and anti-proliferation actions against vascular smooth muscle cells and myofibroblasts. Therefore, CNP is a potential therapeutic agent for the prevention of restenosis following angioplasty. The current study investigated whether local delivery of CNP, even at microgram levels about three orders of magnitude lower than doses (high milligram levels) used for systemic administration in the previous study, attenuates neointimal hyperplasia. The rabbit iliac artery was denuded, and then CNP (100 microg, n = 5) or control vehicle (n = 5) was administered locally over 20 min, via a local drug delivery catheter. During drug delivery, blood pressure was monitored with a high-fidelity micromanometer catheter. There was no significant decrease in arterial pressure immediately after the CNP administration. Four weeks after the treatment, computer-assisted morphometric analysis revealed significant reduction in the intimal area (CNP 0.44 +/- 0.27 versus control 0.96 +/- 0.20 mm2, p < 0.01), but no changes in the medial area (CNP 0.93 +/- 0.23 versus control 0.79 +/- 0.29 mm2, p = NS). This resulted in a significant decrease in the ratio of the intimal area to the medial area in CNP-treated vessels compared with control vessels (CNP 0.45 +/- 0.26 versus control 1.40 +/- 0.66, p < 0.05). Local delivery of a single low dose of CNP effectively inhibits neointimal hyperplasia with a minimal likelihood of compromising hemodynamics. Considering its multipotent actions and its role as an important regulator of the vascular system, this treatment may have a therapeutic advantage for clinical use.

Heparin and coumadin versus acetylsalicylic acid for prevention of restenosis after coronary angioplasty

The purpose of the present study was to determine whether postprocedural antithrombotic therapy with prolonged heparin infusion followed by 6 months of oral anticoagulation in addition to acetylsalicylic acid (ASA) reduces the incidence of angiographic restenosis after successful PTCA. One hundred ninety-one patients with uncomplicated PTCA were randomized into two groups: one group was discharged with ASA 100 mg only (G1) and the other group was additionally treated with 12-24 hr of heparin infusion and overlapping oral anticoagulation with coumadin for 6 months (G2). The two groups were comparable with respect to age, gender, coronary risk profile, clinical presentation, and angiographic lesion characteristics. Stents were implanted in 33% and 36% of the G1 and G2 patients, respectively. In-hospital myocardial infarction occurred in 4% of the G1 and 3% of the G2 patients. One patient in G1 died of subacute stent thrombosis (day 3). Six-month angiographic follow-up was obtained in 90% of G1 patients and 94% of G2 patients. Restenosis occurred in 30% and 33% of the patients and mean diameter stenoses at follow-up were 40% +/- 28% and 39% +/- 24%, respectively. Thrombin inhibition with heparin infusion followed by 6 months of oral anticoagulation did not reduce angiographic restenosis among patients undergoing PTCA with or without stent implantation. The occurrence of acute ischemic complications was also comparable in the two groups.

Surface modification of liposomes for selective cell targeting in cardiovascular drug delivery

Cardiovascular disease processes such as atherosclerosis, restenosis, and inflammation are typically localized to discrete regions of the vasculature, affording great opportunity for targeted pharmacological treatment. Liposomes are potentially advantageous targeted drug carriers for such intravascular applications. To facilitate their use as drug delivery vehicles, we have considered three components of liposome design: (i) identification of candidate cell surface receptors for targeting; (ii) identification of ligands that maintain binding specificity and affinity; and (iii) prevention of rapid nonspecific clearance of liposomes into the reticuloendothelial organs. In this report, we describe our work in developing liposomal surface modifications that address both targeting and clearance. An arginine-glycine-aspartic acid (RGD) containing peptide was used as a model ligand to target liposomes to the integrin GPIIb-IIIa on activated platelets. Additionally, oligodextran surfactants incorporated into liposomes provided insight into the effect of vesicle perturbations on liposome clearance, and the importance of molecular geometry in designing oligosaccharide surface modifications. Together these studies demonstrate the feasibility of using peptides to guide liposomes to desired receptors, and illustrate the influence of vesicle stability on liposome interactions in vivo. Furthermore, they underscore the importance of simultaneously considering both targeting specificity and vesicle longevity in the design of effective targeted drug delivery systems.

Rationale for coronary artery radiation therapy

Within the past decade, focus on radiation to prevent restenosis has moved from a concept developed in the animal laboratory to a clinical treatment. The initial evaluation of coronary artery radiation therapy focused on changes in the function of the artery or lesion formation following overstretch balloon injury in pigs. A number of concepts emerged from this work: (1) radiation inhibits neointima formation in a dose-dependent fashion, (2) radiation prevents negative remodeling, (3) radiation does not reverse established injury, (4) low dose irradiation in an injured area may be injurious, (5) radiation is a useful adjunct to stenting, (6) benefits of radiation in animal models at 6 months are less pronounced than at 1 month, (7) radiation delays healing, (8) permanent stents and radiation delivered from external sources may have very different effects on restenosis, and (9) radiation interferes with vessel wall function. More recent studies of irradiation have looked at the molecular biological effects of radiation in hopes of understanding how this therapy works, and how it may be improved. This article attempts to summarize the known animal and cellular work on radiation in preventing restenosis.

Flufenamic acid: growth modulating effects on human aortic smooth muscle cells in vitro

PURPOSE

The aim of the study was to examine the effects of flufenamic acid on proliferation, clonogenic activity, migratory ability, cell-cycle distribution, and p44/42-mitogen-activated protein kinase (MAPK) expression on serum-stimulated human aortic smooth muscle cells (haSMCs) in vitro.

MATERIALS AND METHODS

HaSMCs were treated with flufenamic acid in three different doses (40 micromol/L, 200 micromol/L, 400 micromol/L) for 4 days, and then flufenamic-acid-free culture medium was supplemented every 4 days until day 20 after initial treatment. The growth kinetics were assessed. Cell-cycle analysis was performed by flow cytometry. The clonogenic activity was evaluated with use of colony formation assays. The migratory ability was investigated by stimulation with platelet derived growth factor (PDGF-BB) in 24 well plates with 8-microm pore membrane inserts. The p44/42 MAPK was detected by Western blot technique.

RESULTS

Flufenamic acid inhibited the proliferation (400 micromol/L treatment over 4 d; 179,700 +/- 49,800 vs 747,900 +/- 144,000; P <.001), clonogenic activity (400 micromol/L treatment over 4 d; 1 +/- 0.3 vs 50 +/- 1.4; P <.001) and migratory ability (400 micromol/L treatment over 4 d; 8 cells +/- 2 vs 48 cells +/- 15; P <.001) of haSMCs in a dose-dependent manner. Cell-cycle analysis revealed a G2/M-phase block (400 micromol/L treatment over 4 d; 28.9 +/- 1.5 vs 9.5 +/- 3.2; P <.001). The expression of p44/42 MAPK was reduced for a treatment with 400 micromol/L flufenamic acid (controls, 427 BLU +/- 0.305 vs treatment group, 190 BLU +/- 106; P <.05)

CONCLUSION

Flufenamic acid inhibits the proliferation and migration of haSMCs. Further experiments with animal models concerning stenosis and restenosis are necessary to evaluate the potential of this promising drug.

tPA via infusion catheters followed by continuous IV infusion for 3 days prevents intimal hyperplasia after balloon injury

A rabbit model was used to examine the effects of tissue plasminogen activator (tPA) on development of intimal hyperplasia following balloon injury. Thirty-two hereditary hypercholesterolemic (KHC) rabbits underwent percutaneous transluminal coronary artery balloon catheterization and injury to the common iliac artery, after which they were divided into four groups: untreated (control); Dispatch catheterized-30 minutes local saline delivery [D(+)-tPA(-)]; D(+)-30 minutes local tPA delivery (0.6 mg/kg) [D(+)-tPA(30 min)]; and D(+)-30 minutes local tPA + 3 days intravenous infusion (0.6 mg/kg/24 h) [(D(+)-tPA(30 min + 3 d)]. Twenty-eight days later, the intimal cross-sectional areas of all three Dispatch catheterized groups were significantly smaller than those of control groups, as were the intimal/medial area ratios. Moreover, the intima/media ratios of the D(+)-tPA(30 min + 3 d) group were significantly smaller than those of the D(+)-tPA(-) group. Thus, local delivery of tPA via Dispatch catheters followed by continuous intravenous infusion of tPA for 3 days prevented intimal hyperplasia after angioplasty.

Controlled release of clot-dissolving tissue-type plasminogen activator from a poly(L-glutamic acid) semi-interpenetrating polymer network hydrogel

With the aim of developing an effective therapeutic modality for treatment of thrombosis, a tissue-type plasminogen activator (t-PA)-loaded porous poly(L-glutamic acid) (PLGA) semi-interpenetrating polymer network (semi-IPN) hydrogel was developed as a possible local drug delivery system. Porous structure of hydrogel was essential in this system to yield a large surface area so that t-PA release could be facilitated. This semi-IPN hydrogel was prepared using the method of free-radical polymerization and crosslinking of polyethylene glycol (PEG)-methacrylate through the PLGA network. Sodium bicarbonate (NaHCO(3)) was added to function as a foaming agent under acidic conditions, rendering the semi-IPN hydrogel to be porous. While the added NaHCO(3) provided gas foam in the reaction mixture, the pH in the hydrogel increased to about 7 to 8, which stimulated the polymerization. The porous structure that was presented at both the surface and sublayer was stabilized during hydrogel formation and freeze-drying. The hydrogel thus prepared possessed a porous structure of 10-20 microm in diameter, as determined by scanning electron microscopy. Results showed that the above hydrogel preparation process did not significantly alter the specific activity of the entrapped t-PA with regard to plasminogen activation and fibrin clot lysis ability. The t-PA release from this semi-IPN hydrogel was examined by measuring the plasmin activity using the chromogenic substrate S-2251. Findings in this paper demonstrated that the porous structure of the hydrogel facilitated t-PA release when compared to the dense structure. Aside from the porous structure, other factors including the content of the crosslinker, PLGA and t-PA could all be varied to regulate t-PA release from the hydrogel. These results suggest that a porous PLGA semi-IPN hydrogel could potentially be a useful local delivery system to release active t-PA primarily at the site of a thrombus.

Local intra-arterial drug delivery for prevention of restenosis: comparison of the efficiency of delivery of different radiopharmaceuticals through a porous catheter

RATIONALE AND OBJECTIVES

Several radiopharmaceuticals were administered through a porous balloon catheter to compare the absolute amount deposited and the retention in the vessel wall. The reported efficiency of local drug delivery ranges from 0.001% to 0.1%, with poor retention after 24 hours.

METHODS

An endothelin derivative (n = 6), pertechnetate (n = 6), hexamethylpropylene amineoxime (HMPAO) (n = 5), ethyl cysteinate dimer (ECD) (n = 5), and tin colloid (n = 5) were labeled with 185 MBq/mL 99m-technetium. After balloon denudation of the infrarenal aorta in 27 New Zealand White rabbits, 100 microL of each agent was administered through a porous balloon at a pressure of 4 bar. Dynamic and static whole-body scintigrams were obtained for 24 hours. The infrarenal aorta was excised and the activity calculated in a gamma counter.

RESULTS

Apart from their retention in the region of local administration, the radiopharmaceuticals showed different distribution patterns. The highest regional tracer retention was observed with HMPAO. After administration of HMPAO, a significant difference between regional (vessel wall plus surrounding tissue: 14.5% of injected dose [ID]/24 hours) and local (vessel wall: 1.8% ID/24 hours) delivery was found. In contrast, ECD was eliminated quickly (local retention after 24 hours = 0% ID). The retention efficiencies were HMPAO > endothelin derivative > tin colloid > pertechnetate > ECD.

CONCLUSIONS

The different physicochemical and pharmacokinetic properties of radiopharmaceuticals resulted in different delivery efficiencies after local application.